Method of inhibiting weed growth in corn



United States Patent US. Cl. 71-118 9 Claims ABSTRACT OF THE DISCLOSURE Method of selectively protecting corn plants from undesirable weeds, which comprises applying to the area infested with the latter an effective amount of the henbicidal compound of the formula:

I O C F3 iHa This invention is a continuation-in-part of our copending application Ser. No. 333,198, filed Dec. 24, 1963, now abandoned.

In contrast to other crops, the corn plant is generally sensitive to the conventional herbicides and tends to be injured considerably by the action thereof. When a known herbicide, such as sodium 2,4-dichlorophenoxyacetate, sodium 2-(2,4-dichlorophenoxy)ethanesulfate, or N-(3,4- dichlorophenyl- N,N -dimethylurea is applied to the corn-growing area, considerable damage and the accompanying fall in the yields are unavoidable. Particularly, the pre-emergent soil application of such herbicide tends to form chlorosis in the sprouts, resulting in deformed leaves, poor growth, and poor yields. Some of the germinating plants die. Post-emergent application also inhibits the growth of the plants, although not so remarkable as compared with the pre-emergent application. Moreover, the post-emergent soil application is particularly injurious, as the plants take root shallow in the soil.

One object of this invention is accordingly to provide a novel method of eliminating undesirable weeds from the corn fields where no suitable herbicidal approaches have been developed yet.

Another object of the invention is to provide the most effective method of protecting corn plants from the undesirable weeds without causing any appreciable damage upon the plants to be protected.

Another object of the invention is to provide the most effective herbicidal method for the protection of corn plants from the undesirable weeds, which can be applied either pre-emergently or post-emergently without causing any harmful effects upon the plants to be protected.

Another object of the invention is to provide the most desirable herbicidal method for the protection of corn plants from the undesirable weeds, the once-a-year application of which is effective enough to protect the plants until the harvest titme.

A further object of the invention is to provide the most effective herbicidal method for the protection of corn plants from the undesirable weeds, which has no harmful effect upon human bodies and domestic and aquatic animals, and which displays marked and lasting herbicidal efiect irrespective of climatic conditions.

The above and other objects of this invention are accomplished by applying to the corn fields 3-trifluoromethyl-2-methyl-4-chlorophenoxyacetanilide of the formula:

in the range of 5 to 40 grams per are.

The compound of the above formula is described by Thompson et al. in Botanical Gazette (107, 1946, p. 506), where it is disclosed that this compound displays /3 to /s the inhibitory activity of 2,4-dichlorophenoxy acetic acid on kidney beans. As will be seen from such description, it is evident that the compound is quite poor in herbicidal capacity on the one hand, and on the other, that the compound displays a considerable chemical injury upon the plants to be protected. Moreover, there is no indication in Thompson et al. of the effective use of said compound for the protection of corn plants from the undesirable weeds.

The present inventors have carried out series of experiments in the effective use of the aforesaid 3-trifluorornethyl-2'-methyl 4' chlorophenoxyacetanalide and have found quite accidentally that despite a considerable chemical injury on most of the plants tested, said compound completely eliminates undesirable weeds not only in pre emergent but in post-emergent application without causing any appreciable chemical injury upon the corn plants under examination. This unexpected selective herbicidal ability deserves specific attention, because the corn plant is generally known as quite sensitive to chemical injury. This invention is ibased upon such a new discovery.

The 3-trifluoromethyl-2'-methyl-4-chlorophenoxyacet anilide which is employed in this invention is of crystalline powder having a melting point of 146 to 146.5 C. It is insoluble or hardly soluble in water, petroleum, carbon tetrachloride, etc., but easily soluble in alcohol, acetone, tetrahydrofuran, N-methyl pyrrolidone, dimethylformamide, -butyrolactone, etc.

The 3-trifiuoromethyl-2'-methyl-4'-chlorophenoxyacetanilide of this invention can be easily synthesized according to various methods. For instance, said compound may be prepared by reacting 2-methyl-4-chlorophenoxy acetic acid halide with S-trifiuorornethylaniline. The reaction is carried out at a temperature bet-ween 0 to 40 C., preferably between 0 to 5 C., in the presence of a solvent, such as acetone, benzene, chloroform, or tetrahydrofurane. Hydrogen chloride acceptors, such as pyridine, sodium carbonate, and the like, may be added to accelerate the reaction. The desired 3-trifluoromethyl-2'-methyl-4 chlorophenoxyacetanilide can also be obtained by conventionally reacting 2-methyl-4-chlorophenoxy acetic acid per se or its anhydride with 3-trifiuoromethylaniline.

The herbicidal compositions of this invention having said 3-trifluoromethyl 2' methyl-4-chlorophenoxyacet anilide as the main effective ingredient are applied to the corn plant field at rates varying from 5 to 40 grams per are, preferably in the range of 7 to 20 grams per are, on the basis of the main effective ingredient. Application of higher than 40 grams per are tends to increase chemical damage on the plants to be protected, and that of lower than 5 grams per are fails to produce expected herbicidal effect.

The 3 trifiuoromethyl-Z'-methyl-4'-chlorophenoxyacetanilide of this invention is formulated for herbicidal use either as dusts, wettable powders, grains, or concentrated emulsifiable solution. Depending upon the type of formulation for use, there is added any of the conventional carriers which include inactive carriers, such as talc,

3 kaoline, bentonite, sericite, etc.; cationic, anionic, and nonionio surface active agents; spreaders, and organic solvents.

The herbicidal compositions containing said 3-trifiuoromethyl-'2'-methyl-4'-chlorophenoxyacetanilide as the main effective ingredient may be applied to the field of the corn plants either in the pre-emergent or in the post-emergent stage of growth thereof. But generally speaking, preemergent application is most desirable and eifective, as the weeds are completely eliminated in their germinating or emergent stage and the growth of the weeds are completely inhibited until the harvest time of the corn. In preemergent application, the herbicidal composition is applied to the soil by spraying or soil incorporation. But it is desirable to apply the composition onto the surface of the soil.

In post-emergent application, the herbicidal composition of this invention is applied to the soil or the leaves of the corn plants to be protected and of the weeds to be eliminated. But it is desirable to apply the composition onto the surface of the soil, although it may be applied to the soil by soil incorporation.

Climatic conditions have hardly any substantial effect upon the herbicidal ability of the herbicidal compositions of this invention, namely said herbicidal compositions may be applied even at a temperature below 20 C. or under exceedingly damp conditions.

The weeds which can be eliminated with the herbicidal compositions of this invention include such broadleaf oleracea), common chickweed (Sterallia media), and rag weed (Ambrosia! artem isiifolia) seeds, 10 grains each.

Two days after seeding, a wettable powder consisting of Parts by wt. 3 trifiuoromethyl 2 methyl-4'-chlorophenoxyacetanilide 25 Kaolin l 60 Sodium dodecylbenzene sulfonate 10 Sodium ligninsulfonate 5 was diluted with water and uniformly sprayed onto the surface of the top layer in the order of 5 to grams per are on the basis of the main effective ingredient. Examination was carried out for chemical damage on the crops 3 weeks after application and for herbicidal effects on the weeds 4 Weeks after application. Findings are shown in Table 1 below.

Test 2.--Leaf application TABLE 1.HERBIOIDAL EFFECT RATING Composition of this invention (grams/are) 2, 4-D (grams/are) Pro-emergent 0 0 0 0 0 0 0 0 1 1 1 2 1 2 3 3 0 1 1 2 l 1 1 1 1 2 3 3 0 1 1 2 l 1 0 1 2 3 3 3 1 1 2 2 1 2 1 1 1 2 3 3 1 1 2 2 1 1 1 1 1 2 3 3 0 1 2 2 1 1 0 1 3 3 3 3 1 2 3 3 0 1 0 1 2 3 3 3 1 2 3 3 2 3 3 3 2 3 3 3 2 2 3 3 2 3 3 3 smartweed 3 3 3 3 2 2 3 3 1 2 2 3 Amaranthua albus- 3 3 3 3 2 3 3 3 2 3 3 3 Goosefoot 3 3 3 3 2 3 3 3 2 3 3 3 Common purslane- 2 3 3 3 2 2 3 3 1 2 2 3 Common chickweed 3 3 3 3 2 2 3 3 2 3 3 3 Ragweed 3 3 3 3 3 2 3 3 2 3 3 3 Narrowleaf. 2 2 3 3 1 1 2 2 1 1 1 1 Broadleaf 3 3 3 3 2 3 3 3 2 3 3 3 1 2, 4-D: sodium 2, 4-diehlorophenoxyaeetate.

(A) SELECTIVITY TESTS Test l.-Pre-emerge nt application In an open box, 150 cm. by 20 cm. and 15 cm. deep, was laid soil. In the surface layer of this bed were planted 1 cm. deep corn, millet, rye, radish and tomato seeds, 10 to 20 grains each. Upon the surface of this layer was uniformly placed 5 mm. deep another layer of the same soil incorporating large crabgrass (Digitaria sanguimalis), green foxtail (Setaria virz'dis), jointed fiatsedge (Cyprus microiria), smartweed (Polygonum blumei), Amaranthus albus, Chenopodiumv album, common purslane (Portulaca (B) INJURY TEST ON CORN Test 3.--Preemergent soil surface broadcast application A test plot previously infested with narrowleaf weeds, such as large crabgrass (Digitaria sanguimalis), goose grass (Eleusine indica), and green foxtail (Setaria viridis), and broadleaf weeds, such as smartweed (Polygonum blumei), common purslane (Portulaca oleracea), Amaranthus albzls, and Chenopodium album, was seeded with corn. Three days after seeding, the solution prepared in the same manner as in Test 1 was sprayed onto the surface of the plot at rates varying from 5 to 40 grams per are in terms of the main eifective ingredient.

Test 4.Soil incorporation Another plot previously infested with the same weeds as specified in Test 3 and seeded with corn was treated in the same manner as in Test 3. Following application, the herbicidal composition applied was uniformly incorpo rated into the soil by ploughing.

Test 5a.-Post-emergent application-1 Another plot previously infested with the same weeds as specified in Test 3 was seeded with corn. When the crops and the weeds reached the 3 to 4 leaf stage about 4 weeks after seeding, the herbicidal solution as prepared in the same manner as in Test 1 was applied to the corn plants by soil application and to the weeds by leaf application.

Test b.-Post-emergent application2 Another plot previously infested with the same weeds as specified in Test 3 was seeded with corn. When the crops and the weeds reached the 3 to 4 leaf stage, the weeds were mown with the weeder, and the herbicidal solution as prepared in the same manner as in Test 1 was applied to the soil as in Test 511.

The results of Test 3 to 5 were all examined 3 weeks after application for chemical injury on the corn plants and for herbicidal eifects on the narrowleaf and broadleaf Weeds. Findings are set forth in Table 2 below. The rating scales employed were:

Percent herbicidal efifect:

Number of weeds in untreated plot number of weeds in treated plot 100 Number of weeds in untreated plot Chemical injury upon the corn plants: no injury; slight injury; moderate injury; i+++: severe injury.

of said herbicidal compound to be applied ranges from 7 to 20 grams per are.

3. The method of selectively inhibiting the growth of weeds as claimed in claim 1, wherein said herbicidal compound is applied to the soil before the germination ot the seeded corn.

4. The method of selectively inhibiting the growth of weeds as claimed in claim 3, wherein said herbicidal compound is applied onto the soil surface.

5. The method of selectively inhibiting the growth of weeds as claimed in claim 1, wherein said herbicidal compound is applied to the corn-growing area after germination of the corn plants.

6. The method of selectively inhibiting the growth of weeds as claimed in claim 5, wherein said herbicidal compound is applied onto the soil surface.

7. The method of selectively inhibiting the growth of weeds as claimed in claim 5, wherein said herbicidal compound is applied to the corn-growing area during the growing period of the corn plants.

8. The method of selectively inhibiting the growth of weeds as claimed in claim 7, wherein said herbicidal compound is applied to the corn-growing area during the growing period of the corn plants and preand early postemergent period of the weeds.

9; The method of selectively inhibiting the growth of weeds as claimed in claim 7, wherein said herbicidal compound is applied onto the soil surface.

TABLE 2: HERBICIDAL EFFECT AND INJURY ON CORN PLANTS Herbicidal efiect (percent) Grams ury Test Composition per are Narrow leaf Broad leaf on corn Remarks on injury 5 90 100 No injury. 3 Composltion of this 1nvent1on.-- 10 100 100 Do. 20 100 100 D0. 100 100 D0. DCMU 1 20 100 100 Chlorosis formed on sprouts; poor growth. SES 2 20 70 100 Most leaves deformed; marked fall in yields.

5 0 40 No injury. 4 Composition of this invention 10 Do. 20 90 95 Do. 40 100 100 Do. DCMU 20 95 95 Died after sprouting. SES 20 100 Most leaves deformed; poor growth.

5 0 70 No injury. 5a Composition of this inventlon. 10 0 80 Do. 20 80 100 Do. 40 100 100 Do. DCMU 20 50 50 Growth slightly inhibited; slight fall in yields. SES 20 10 30 Sprouts deformed; slight tall in yields.

5 70 N i 5b Composition of this invention 10 o 1 3 i 20 100 100 Do. 40 100 100 D0. DCMU 20 100 100 Growth slightly inhibited; slight fall in yields. SES 20 80 100 Sprouts deformed; slight fall in yields. 1 DCMU: N-(3,4-dichlorophenyl)-N, '-dimethylu.rea. 2 SES: sodium 2-(2,4-diehlorophenyl) ethanesulfate.

We claim: References Cited 1. Method of selectively inhibiting the growth of the U NITED TATES PATE T undesirable weeds until the harvest tlme of corn, 'WhlCh S N S comprises applying to the corn-growing area 3-trifluoro- 3,439,018 4/1969 Brooke's et X methyl 2' methyl 4' chlorophenoxyacetanilide of the 3,414,400 12/1963 Watollabe et a1 71 118 formula:

in the range of 5 to 40 grams per are.

2. The method of selectively inhibiting the growth of weeds as claimed in claim 1, wherein the effective amount OTHER REFERENCES Thompson et al., Botanical Gazette, vol. 107, pp. 476-501 (pages 479-482, 486, 490, 494, 495, 497-500, 503, 505-506 particularly relied upon), 1946.

JAMES 0. THOMAS, JR., Primary Examiner 

